7.
Definitions
Heel contact with the ground on the upstream side
Toe contact on the downstream side
Abutment Sides of the valley on which the structure of the dam rest
Galleries small rooms like structure left within the dam for checking
operations
Diversion tunnel Tunnels are constructed for diverting water before the
construction of dam This helps in keeping the river bed dry
Spillways It is the arrangement near the top to release the excess water
of the reservoir to downstream side
Sluice way An opening in the dam near the ground level, which is used
to clear the silt accumulation in the reservoir side

8.
Advantages of Dam
Irrigation
Water Supply
Flood Control
Hydroelectric
Recreation
Navigation
Dams gather drinking water
for people.
Dams help farmers bring
water to their farms.
Dams help create power
and electricity from water.
Dams keep areas from
flooding.
Dams create lakes for people
to swim in and sail on.

9.
Disadvantages of Dam
Dams detract from natural settings, ruin nature's work
Dams have inundated the spawning grounds of fish
Dams have inhibited the seasonal migration of fish
Dams have endangered some species of fish
Dams may have inundated the potential for
archaeological findings
Reservoirs can foster diseases if not properly
maintained
Reservoir water can evaporate significantly
Some researchers believe that reservoirs can cause
earthquakes

12.
Three Gorges Dam
Type: Concrete Gravity Dam
Cost: Official cost $25bn - actual
cost believed to be much higher
Work began: 1993
Due for completion: 2009
Power generation: 26 turbines on
left and right sides of dam. Six
underground turbines planned for
2010
Power capacity: 18,000
megawatts
Reservoir: 660km long,
submerging 632 sq km of land.
When fully flooded, water will be
175m above sea level
Navigation: Two-way lock system
became operational in 2004.
One-step ship elevator due to
open in 2009.

16.
Hoover Dam
Location: Arizona and Nevada, USA
Completion Date 1936
Cost 165 million
Reservoir Capacity 1.24 trillion cubic feet
Type Arch/ Gravity
Purpose: Hydroelectric power/flood control
Reservoir: Lake Mead
Materials: Concrete
Engineers: Bureau of Reclamation
The Hoover Dam is a curved gravity dam. Lake Mead
pushes against the dam, creating compressive forces
that travel along the great curved wall. The canyon
walls push back, counteracting these forces. This
action squeezes the concrete in the arch together,
making the dam very rigid. This way, Lake Mead can't
push it over.
Today, the Hoover Dam is the second highest dam in
the country and the th highest in the world. It
generates more than four billion kilowatt-hours a
year, that's enough to serve . million people!

29.
Arch Dam
An arch dam is a curved dam
which is dependent upon arch
action for its strength.
Arch dams are thinner and
therefore require less
material than any other
type of dam.
Arch dams are good for sites
that are narrow and have
strong abutments.

61.
Buttress Dam
Buttress Dam
: is a gravity dam reinforced by structural supports.
Buttress
:a support that transmits a force from a roof or wall to another
supporting structure.
This type of structure can be considered even if the foundation
rocks are little weaker.

67.
A coffer dam during the
construction of locks at
the Mongomery Point
Lock and Dam.
Miscellaneous Types of Dam
Coffer Dam

68.
Dam Failure
Tailing Dam at Aznalcollar Mine, Spain
April 25, 1998: the tailings dam at the Aznalcollar
mine near Sevilla, Spain failed. This has had BIG
societal implications -- the toxic waste has killed
many fish and birds and flooded thousands of
hectacres of farmland.
February 26, 1999 marks the 27th anniversary of the failure of another
tailings dam on Buffalo Creek, West Virginia 125 peoople were killed
and 4,000 were left without homes. The dam failure was compounded
by the fact that it was waste that was escaping; the waste caught fire
and an explosion eventually occured.

70.
Dam Failure
June 5, 1976: the failure in the Teton Dam led to flooding in the
cities of Sugar City and Reburg in Idaho. The dam failure killed 14
people and caused over $1 billion in property damages.
The dam failed because the bedrock was not strong enough to
support the structure. Currently the dam is once again used for
hydroelectric power.
Teton Dam, Idaho

71.
Dam Failure
July 17 1995 : a spillway gate of Folsom Dam failed, increasing
flows into the American River significantly The spillway was
repaired and the USBR carried out an investigation of the water
flow patterns around the spillway using numerical modelling
No flooding occured as a result of the partial failure, but flooding
is still a major concern for this area It seems that the Folsom Dam
may be due for a height increase as an answer to this concern
Folsom Dam, USA

87.
Issues:
 Time-Value of Money
 Today’s Costs vs. Tomorrow’s Benefits
 Must Discount the value of future benefits
 The Discount rate is like the interest rate
 Incorporates the risk of the project, and the alternative
uses of the money, such as investing the money
somewhere else.

88.
Impacts of Dams
 Barriers to fish and boat movement
 Salmon in the west, Shad in the east
 Must build locks to move boats around dams
 Sediments build up in reservoir
 Farmland along the Nile and Mississippi Rivers
depended on these for soil improvement, and the
Delta needs these to keep the ocean out
 Many cities, farms, and people must be relocated

89.
FERC Relicensing
 The Federal Energy Regulatory Commission (FERC)
regulates private dams (such as Georgia Power
dams).
 In order to get or renew a permit, the operator has
to explain how the dam benefits the public.
 FERC can give the original permit to anyone.
 When renewing a permit, FERC can give it to the
builder, or to anyone else they choose.
 Many Georgia Power dams must have their permits
renewed, and are finding ways to improve their
performance so they can get their permit renewed.

90.
Figure 7.12 This scene in Wanxian, the largest of the relocation cities
affected by Three Gorges Dam, called Sanxia Ba in China (San meaning
“three,” Xia meaning “Gorge,” and Ba meaning “Dam”).

91.
Figure 7.13 This tributary of the Yangtze River flows through the narrow
canyon called Xiao Sanxia (Lesser Three Gorges) and will be flooded after
completion of the Three Gorges Dam.

92.
Dams and Locks for Navigation
 Problem with dams blocking rivers
 Historical use of rivers by boats to transport goods.
 With a new dam in the way, the barge operators are put
out of business.
 Protests build for providing a way around the
obstruction.

93.
Figure 7.14 Main-river dams form a staircase of reservoirs that stretch the
entire length of the Tennessee River.

94.
Figure 7.15 Chickamauga Lock and Dam, located on the Tennessee River
near Chattanooga, Tennessee, is a major lock in the TVA navigation system.

99.
Athens Poultry Industry
 Employs
 150 workers per shift (three shifts) at about $10/hr
 Several dozen supervisors at about $20/hr
 This is a payroll of over $15,000,000 per year
 Water Use
 They process about 200,000 birds per day
 This requires about 7 gallons per bird
 Which is 500 million gallons per year
 Water value
 is 3 cents per gallon
 not counting taxes and other community benefits.

110.
Reservoirs
 A reservoir is an artificial lake called man-made reservoir. It can be
formed by building a dam across a valley, by excavating the land or
by surrounding a piece of land with dykesand diverting a part of the
river flow into the reservoir. The water is stored in the reservoir
and can be used for irrigation, hydro-power or as a water source for
domesticor industry use. Man-made reservoirs are also very
effective constructions to control unexpected floods (see also
stormwater management).
 A reservoir is fed by precipitation, rainwater runoff or from a
constant flow of a river. Water loss can occur due to evaporation
(especially in arid regions) and depending on the reservoir bottom
due to percolation (small reservoirs are often lined). Sediments
from rivers or surface runoff can reduce the storage volume of a
man-made reservoir significantly (FAO 1992).

112.
Reservoirs
 Water stored in a valley usually has a higher level than the valley
bottom downstream of the dam. Because of this difference in level,
the valley can be irrigated by a gravity system or other distribution
systems. Water can be taken from the reservoir via a concrete or
steel pipe.
 This pipe connects the reservoir to an irrigation canal downstream.
A valve is usually located on the upstream end of the pipe to
control the discharge of water into the canal (FAO 1992). The
kinetic energy of reservoirs is often used to produce electricity (see
also hydropower small-scale and hydropower large-scale).

113.
Comparison of the riverbed landscape between upstream and
downstream reaches of the Yasugawa Dam in the Yasu River in central
Japan. The dam is as old as 53 years and the distinctive riverbed
armouring can be observed. White part of rocks indicates thick
accumulation of organic matter originated from the reservoir. Source:
TAKEMON (2006)

114.
Reservoirs
 Where no such water-body previously existed the presence of a
reservoir in a drainage basin and the abstraction of significant water
amounts for storage upstream significantly impacts the watercourse,
the flora and fauna, and the human inhabitants in the drainage basin.
 These potential impacts should be identified and thoroughly examined
prior to reservoir construction, in order to comprehensively assess the
total value of the reservoir project.
 Procedures to identify and properly evaluate potential environmental,
social and economic consequences of reservoir construction involve so-
called „Environmental Impact Assessment‟ (EIA). Such an assessment is
now obligatory by law in many countries for all new dam constructions
(UNEP 2000).

115.
Reservoirs
 Ecological impacts of reservoir dams have been reported from
various aspects such as barrier for migratory animals like
anadromous fish, eutrophication of reservoirs by plankton
blooming, decreasing flow volumes in tail waters, stabilisation of
flow regimes by flood peak cut, changes in thermal regimes of river
water, river bed degradation and increase in substrate grain size by
sediment trapping, etc. (TAKEMON 2006).
 Furthermore big dams and extraction of water (e.g. for spate
irrigation) can create riparian conflicts (see water conflicts). Also
read the paragraph “Impact on Environment” in the rivers
factsheet.

116.
Basic Design Principles
Adapted from UNEP (2000)
 Like lakes, reservoirs range in size from pond-like to very large
water-bodies (e.g. Lake Powell, U.S.A.). The variations in type and
shape, however, are much greater than for lakes. The term
„reservoir‟ includes several types of constructed water-bodies
and/or water storage facilities:
 1. Valley reservoirs – created by constructing a barrier (dam)
perpendicular to a flowing river.
 2. Off-river storage reservoirs – created by constructing an
enclosure parallel to a river, and subsequently supplying it with
water either by gravity or by pumping from the river.

118.
Basic Design Principles
Adapted from UNEP (2000)
 The latter reservoirs are sometimes called embankment or bounded
reservoirs, and have controlled inflows and outflows to and from
one or more rivers.
 In addition to single reservoirs, reservoir systems also exist, and
include cascade reservoirs - consisting of a series of reservoirs
constructed along a single river, and inter-basin transfer schemes –
designed to move water through a series of reservoirs, tunnels
and/or canals from one drainage basin to another.

119.
Pumping from a Reservoir for
Irrigation
 The fields located around the reservoir upstream of a dam or surrounding a
natural lake are higher than the reservoir or lake's water table. Here
irrigation is only possible with the help of pumping stations, manual or
motorised pumping.
 The water level in the reservoir is usually highest at the end of the rainy
season, and lowest at the end of the dry season or the irrigation season.
Pumps installed at reservoirs and lakes must be able to handle these
fluctuations, which are not only vertical, but even more pronounced
horizontally, because the water recedes back to the lowest parts of the
reservoir.
 A dead branch of a river can also be made to function as a reservoir. The
branch is filled with water during the wet season and closed off during the
dry season so that the stored water may be used. Due to the low water
level, pumps are normally needed to irrigate fields from such a reservoir.

120.
Pumping from a Reservoir for Irrigation
 A small reservoir in the hills of Tepoztlán (Morelos, Mexico), which is mainly filled
by precipitation catchment. The water is extracted by gravity and is protected by a
fence to avoid contamination from animals or unauthorised use. The reservoir is
sealed with an impermeable liner. Source: B. STAUFFER (2009)

121.
Operation and Maintenance
 Because reservoirs are man-made water-bodies, they are more amenable to
artificial operation and regulation than lakes. As previously noted, operational
possibilities unique to reservoirs include the ability to discharge known
volumes of water at predetermined times, and selective discharge of water from
different water layers within the reservoir. This must be planned carefully as it
directly impacts the environment as described above. Also read the document
“Reservoir Operations and Managed Flows” (WMO and GWP 2008).
 Dams, especially the very large ones, must be checked regularly to ensure their
stability and security. Furthermore, many man-made water reservoirs are
affected by high sedimentation rates.
 The accumulation of sediments in the reservoir reduces the main reservoir
asset i.e. its volume capacity. Moreover sediments can negatively affect
pumping and hydropower equipment. Therefore the designers should
consider the soil erosion and sediment transport (CHANSON and JAMES
1998). There are several approaches to minimize or deal with sedimentation.

122.
Operation and Maintenance
 When a reservoir serves different functions it is nearly impossible to operate
each function at its maximum level. For example, a reservoir that provides
irrigation, power generation (see small scale and large scale hydropower), flood
control, and recreational use may cause conflicting demands by its users
(WATERENCYCLOPEDIA 2011).
 Health Aspects
 Faecal pollution and other contamination of reservoirs has to be prevented by
wastewater treatment and buffer zones in case of non-point sources of
pollution (see also the factsheets on lakes or invalid link). If the reservoir is also
used as a source of drinking water, please also check water purification as a
measure to protect human health.
 It should also be considered, that surface water sources can lead to mosquito
breeding..